High frequency signaling system



April 7, 1942. H. RCDER 2,279,062

' HIGH FREQUENCY SIGNALING SYSTEM Filed April 29, 1933 2 Sheets-Sheet 1Fig. I.

Inventor.- Hans Rock-:17

April 7, 1942. H. RODER BIGH FREQUENCY SIGNALING SYSTEM 2 Sheets-Sheet 2Filed April 29, 1953 7. 10 x C05 r-cos 29 PERCENTAGE CHANGE IN ANTENNACAPACITY Inventor:

Hans Rock-2r: 139 MW His Attomweg.

Patented Apr. 7, 1942 s'rrs FFICE HIGH FREQUENCY SIGNALING SYSTEM YorkApplication April 29, 1933, Serial No. 668,595

16 Claims.

My invention relates to high frequency signaling systems and moreparticularly to antenna systems of the directive type.

It has for one of its objects to provide such a system capable ofmaintaining constant directivity irrespective of variations in theantenna constants caused by extraneous influences such, for example, asvariations produced by weather conditions.

A further object of my invention is to provide means whereby currentsupplied from a common source to diiferent antennae may be automaticallymaintained in desired phase relation irrespective of variations inconstants of the different antennae.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My in ventionitself, however, both as to its organization and method of operation,together with furtherobjects and advantages thereof may best beunderstood by reference to the following description taken in connectionwith the accompanying drawings in which:

Fig. 1 represents a beacon system to which my invention may be applied;

, i Fig. 2illustrates a modification thereof, and

Figs. 3 and 4 illustrate certain characteristics of my invention.

Referring to the drawings, I have shown in Fig. 1 thereof a plurality ofantennae I, 2, 3, and 4 which may be arranged at the corners of asquare, for example, and energized from a common transmitting station 5located at the center of the square. The transmitting station isrepresented as having two output circuits 6 and I, the output circuit 6being connected to transmission lines 8 and 9 of equal length leadingthrough transformers Ill and II respectively to antennae 3 and I, whichare located at diagonally opposite corners of the square. The outputcircuit 1 leads through similar transmission lines I2 and I3 of equallength and transformers I5 and IE to antennae 2 and 4 arranged at theremaining pair of diagonally opposite corners.

. As thus constructed and with antennae 3 and I energized in a desiredphase relation they cooperate to produce a figure eight radiationpattern. Antennae 2 and 4 when similarly energized cooperate to producea figure eight radiation pattern the axis of which lies at an angle of90 to the axis of the radiation pattern produced by antennae I and 3. Inthis way four equisignal zones are produced in directions radi- I atingfrom the beacon at ninety degrees apart and at 45 angles to the axes ofthe two radiation patterns. These equisignal zones constitute coursesalong which aircraft may be guided.

In the operation of such systems it has been found that the courses laidout by the beacon do not remain in fixed position but instead vary to aconsiderable extent. Such variation may be produced by Variation in thephase relation between currents in diagonally opposite antennae whichmay in turn be caused, for example, by weather conditions influencingthe capacity of the different antennae.

In accordance with my invention the system is so adjusted thatvariations in capacity of the difierent antennae do not influence thephase relation between currents in the different antennae with theresult that the courses laid out remain in fixed position.

For an understanding of the manner in which this is effected it may beassumed that all of the systems feeding the antennae are identical. Thenif each system be so constructed that the phase relation between theantenna current Ia and the voltage E1 supplied to the transmission lineremains constant irrespective of variations in antenna capacity thedesired result will be accomplished. Consideration may therefore belimited to the system supplying a single antenna, for example, antenna2.

To determine the manner in which the antenna current Ia. varies withrespect to the voltage E1 both of these quantities may be expressed interms of the current Ix flowing in the primary of the transformer I5,the fixed constants of the system, and the antenna tuning which varieswith the extraneous conditions. These expressions may then beinvestigated to determine the proper tuning of the system relative tothe fixed constants of the system to render the relation between antennacurrent Ia and the voltage E1 supplied to the transmission lineindependent of variations in antenna capacity.

To efiect this calculation it is first realized that, for eflicientoperation, the tuning of the antenna, and its coupling to thetransmission line must be such that the transmission line I2 isterminated in its surge impedance. Thi condition of the system will bereferred to herein as the normal condition of the system from which thesystem deviates due to extraneous influences.

The surge impedance, on account of the high frequency, is a pureresistance and may be designated Z. It can readily be shown that toterminate the transmission line in its surge impedance, the followingrelations must apply:

In these equations Xm is the mutual reactance of transformer l5, R isthe total resistance of antenna circuit, X20 is the total reactance ofthe antenna circuit under normal conditions, Xz is the reactance of theantenna circuit reflected into the primary of the transformer, and Xp isthe total reactance of that portion of the primary circuit of thetransformer at the leftof the line. designated in the drawing Ex, Ix. Itwill be noted that this value Xp includes the reactance of condenser I?which is'inserted for the purpose of securing a desired value of thequantity Xp, as will later be explained.

If we now represent the capacity of the antenna under normal conditionsby C and any change in this capacity due to extraneous influences by dCthen we may write 7 Where. XL represents the total inductive reactance"of the antenna circuit at any instant, Xe represents the totalcapacitive reactance o fthe antenna circuit under normal conditions, Xdcrepresents the instantaneous change in capacity of the antenna circuitdue to extraneous influences and w=21rf where f is the frequency to beradiated. I 7

Eiipressio s as follows for current, In in the. primary of transformer55, andantenna current It, may readily be derived:

1 1 cos +j% sin 6 where 0 represents the length of the transmission lineexpressed in degrees, i. e. in terms or phase displacement betweenvoltages E1 which is supplied to the transmissionline and. the voltageEx at the remote end of the transmission. line, it being assumed thatthe line is. terminat id into its surge impedance.

If the line be properly terminated, then ItZ=Ez and from Equations 1 and2 the following relations may be derived:

and =phase displacement between antenna current Ia and the voltageinduced in the antenna by the current IX when dc=o.

'By substituting Equations 3 and 8 into Equation 6. we. obtain thefollowing expression for, the

- antenna current:

Similarly by substituting' Equations 3 and 9; into Equation 5 we obtain:

E1= 4' Gasman t +am a) (it cos 1// i 29, +1 R In Equations 10-, I l and12 the brilyvariable is y. From Eq ation 4 rte-an be that'thi's variableis a runcnon of the change iiiantenna capacity from the normal ontaner-'1."

Equations 10 and 1-2 are hence the d'si-tedxpressions referring theantenna on rent; the supplied voltage E1 respective rentIx in theprimaryof the trahsfdrrner; expressions indicate these relations in andamplitude, The manner in the 'ntenna current It varies with respect tqthe-subs plied voltage E1 upon var at ons: antenna ca hacity; and the]proper tuning of the antenna; tof minimize this variation, may now bdetermined. These equations may readily be solved graph ical'ly.'inecompiex function Then by drawing the scale S parallel to theimaginary, or vertical, axis at a distance from the imaginary axis anddividing this scale in linear terms of y (or by means of Equation 4 innon-linear terms of 93) We can find the value of W for every value of yby projecting a line from the origin through the different points on thescale S to the circle, in the manner shown at W in Fig. 3. The length ofthis line represents the value of and the vector in coincides with thisline. 7 '7 From Equation 12 we see that the vector E1 may be obtained byadding the quantities W and 1' cos i// (tan and tan t). This latterquantity is imaginary. Therefore, if we measure ofi the quantity cos I/(tan +tan 0) on the imaginary axis of Fig. 3 and connect the point sodetermined with the intersection of the vector W with the circle we havea vector representing E1. We may now indicate on the diagram by 9 theangle between Ix and E1, and by the angle between E1 and 71a.

Now to determine graphically the angle 3 between jIa and E1 for allvalues of antenna capacity it will be necessary to lay ofi thecorresponding values of y on the scale s and complete the triangle bydrawing in the vectors corresponding to E1 and a'Ia as already describedfor every value of y, as indicated by the dotted lines in Fig. 3.

In Fig. 4 are shown a family of curves determined in this way andexpressing the relation between the angle and the percentage change inantenna capacity. In obtaining these curves the following constants wereassumed:

R=6 ohms XL=X00=1000 ohms Length of the transmission line 0=60 Surgeimpedance Z of the transmission line:

80 ohms In determining each curve it was assumed that the antennacapacity C was normally such that the phase angle 1,0 between antennacurrent Ia and the induced voltage had the value indicated on the curve.

From Fig. 4 it will be observed that the curve corresponding to =60shows no variation in produced by variation in antenna capacity. But 60,it will noticed, is the assumed electrical length 0 of the transmissionline. Thus from Fig. 4 it appears that if the antenna be detuned fromresonance to such an extent that the phase angle between antenna currentand voltage is equal to the length of the transmission line expressed indegrees the phase of the antenna current is constant irrespective ofchanges in antenna capacity. In other words the antenna should be sotuned that =9.

That this relation is not a coincidence in a particular case, butapplies in general can readily be seen from Equations 10 and 12. If

be made equal to zero it will be seen from Equations 10 and 12 that thevoltage E 1 and current jIa will be in phase irrespective of the valueof 11. But this term is equal to zero when \//:*0. This generalrelationship is also apparent from Fig. 3 since if the vector 005 w (tan+tan 0) be made equal to zero the vector E1 will fall upon :iIa; i. e.E1 and jIa are in phase irrespective of the value of y.

A further important result is apparent from Equations 10 and 12 if it beassumed that oz-e. From these equations it may be found that I -jE1 =aOO'nStLnt be produced by variation of either. the magnitude or phase ofthe antenna current.

Thus from this consideration the following simple rules may be followedin designing the system.

1. Terminate the transmission line in its surge impedance. 2. Tune theantenna so that =-0.

Each of the antennae circuits includes a load coil 3 which may beemployed to efiect this desired tuning. The condenser I! is employed inthe primary circuit to tune out the reactive component of the antennaimpedance which is reflected through the transformer thereby toterminate the transmission line in its surge impedance.

The efiect of the tuning of the antenna to displace the antenna currentand induced volt age, as above explained, is, in other words, to insertan impedance into the system such that upon any change in reactance ofthe antenna a reactive impedance is presented to the transmission linewhich causes the voltage E5; to vary in phase with respect to thevoltage E1 by an amount just suflicient to maintain the current Ia inconstant phase relation with respect to the voltage E1. That is, theintermediate electrical variables Ex, I1: and induced voltage in theantenna all vary by amounts just sufficient to maintain the desiredconstant phase relation between Ia and E1.

In the above consideration of Fig. 1 it was assumed that the diagonallyopposite antennae were energized with a phase displacement of 180thereby to lay out straight courses. It frequently occurs that it isdesirable to bend the courses. It is therefore necessary to energize thediagonally opposite antennae with phase displacements of less than 180in which case the figure eight patterns become cardioides. This may beeffected in the manner illustrated in Fig. 2. In this figure anartificial transmission line I! is connected in the line extending toone antenna of each pair. This artificial line should have an electricallength equal to the phase displacement from the 180 degree relationdesired between the two antenna currents. For example, if the twoantennae are to be energized with a phase displacement of l-- then theartificial transmission line should have an electrical length equal to pto maintain constant the phase relation and magnitude of the antennacurrents. The antenna, to which the artificial line is connected, shouldbe so tuned that =(0+ The artificial transmission line should be sodesigned that its input and output impedances are equal and so that itsinput and output voltages are equal. Since the theory whereby such anetwork may be designed and constructed is well known, it will not beconsidered here. It'is sufficient to state that the line may be of the Tform, as illustrated, in which the series elements may be inductive andthe shunt element capacitive if the angle (+p) is to be greater than 0or the series elements may be capacitive and the shunt element inductiveif the angle (0+ is to be less than 0.

Since Equations 7 above are derived upon the assumption that theattenuation of the transmission line is negligible the results aboveattained are accurate only when such assumption is proper. In mostpractical cases, however, they are sufliciently accurate. If it beassumed that the attenuation is not negligible, as for example, in caseswhereunderg'roundcable is employed, then the Equations 7 take on thefollowing form:

E1=EI cosh ar-I-IeZ sinh an: 4 (13) I1=I2 cosh aa:+E.T/Z sinh ax where+ifi where a=attenuat1on constant per meter 1 of the line;

6=wavelength constant per meter f x=physical lengthof the lineiii-meters.

am=attenuation of line measured in nepers.

eac=0=electrical length of transmission line in degrees.

If We substitute Equations 13 into Equations 16 andll we obtain:

This equation corresponds to Equation 12. can easily be shown that sinh2azc+j sin 23a: cosh ax+ cos 2130av Since our in most cases is small wemay replace the sin h and cos h by the first terms of their respectiveseries. Equation 14 then becomes 201x 1+cos tan 6 tanh ax= (16)Therefore 2cm 1 cos 20 Equation 14 may be representedin the formof acircle in the same way as was done with Equation 12. The circle diagramwill be the same as Fig. 3 except as will be seen from the Equation 17the vector cos gl/ (tan ip-l-tan 0) will be moved to the left from theposition A to the position B by an amount the fact that the origins ofthe two vectors are spaced apart on the real axis by the amount Tominimize this phase displacement the transmission line should beconstructed with minimum attenuation.

In constructing a system in accordance with my invention it may be founddifficult so to tune the antenna that =-0 where 0 is very large as forexample in excess of 75. In such a case it is desirable to insert anartificial line in the transmission line having series elements ofcapacity thereby to reduce the electrical length of the entire lineincluding the artificial portion to a value which permits practicaltuning in accordance with the desired relations.

While I have mentioned the use of my invention in connection with radiobeacon systems it will of course be understood that it is not limitedthereto but that it is applicable generally in systems where it isdesired to minimize the effect of the extraneous influences upon theantenna. One application is in connectionwith directional broadcasting.Further, while I have shown particular embodiments of myinvention itwill be understood that it is not limited thereto but that modificationsmay be made both in the circuit arrangement shown and in theinstrumentalities employed and that, by the appended claims, I proposeto cover any such modifications as fall within the true spirit and scopeof my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, an antenna, a transmission line connected to saidantenna, said antenna having constants so proportioned with respect tothe operating frequency that the current in the antenna is displaced inphase from the voltage induced in the antenna by an amount equal to theelectrical length of said transmission line.

2. In combination, a transmission line, an antenna, a coupling betweenthe antenna and transmission line arranged to terminate the transmissionline in its surge impedance, and. means of such nature that said antennais detuned from the operating frequency by an amount determined inaccordance with the length of said transmission line.

3. In combination, a transmission line, an antenna, a coupling betweensaid transmission line and antenna whereby voltage is supplied from saidline to said antenna, means so to tune the antenna that the currentflowing therein is displaced in phase from the voltage induced thereinby an amount substantially equal to the electrical length of thetransmission line, and said coupling having an input impedance equal tothe surge impedance of the transmission line.

4. In combination, a transmission line, an antenna, a transformerconnected between the antenna and transmission line, means so to tunethe antenna that the current flowing therein is displaced in phase fromthe voltage induced in the secondary Winding of said transformer by anamount determined in accordance with the length of said transmissionline, and means including said transformer to terminate saidtransmission line in its surge impedance.

5. In a system for operating a plurality of antennae with apredetermined phase displacement between the currents in the difierentantennae, the combination of a source of oscillations, separatetransmission lines connected between said source and said antennae, oneof said antennae being so tuned that the current flowing therein isdisplaced in phase from the voltage supplied to it by an amount equal tothe actual electrical length of its respective transmission line plusthe desired phase displacement between said antenna currents, and anartificial transmission line connected in series with said respectivetransmission line having an electrical length equal to said desiredphase displacement.

6. In combination, an antenna, a transmission line coupled to saidantenna, and means for normally displacing the antenna current from thevoltage induced in the antenna by an amount equal to the electricallength of said transmission line.

7. In combination, an antenna, a source of high frequency oscillations,a transmission line connecting said source with said antenna, and meansto maintain a constant phase relation between the current in saidantenna and the voltage supplied to said transmission line by saidsource during variations in capacitance of said antenna, said meansbeing efiective to maintain said constant phase relation irrespective ofthe magnitude of said variations in capacitance.

8. In combination, source of oscillations, an antenna, a transmissionline extending between said source and said antenna, means normally toterminate said transmission line in its surge im pedance, and means tocause the voltage supplied to the antenna by said transmission line tovary in phase, in instantaneous response to changes in reactance of theantenna, sufiiciently to maintain the antenna current in a constantphase relation with respect to the voltage supplied to the transmissionline.

9. The combination, in a directive radiation system, comprising aplurality of spaced radiators, of means to maintain constant the fieldpattern produced by said radiators, said means comprising a commonsource of oscillations, transmission lines extending from said commonsource to each of said radiators, and means continuously efiective tomaintain the current in each radiator in constant phase relation withrespect to the voltage produced by said source.

10. In combination, an antenna, a transmission line, a coupling betweensaid transmission line and antenna, and means so arranged that upon anychange in capacity of said antenna a corresponding change occurs inimpedance reflected from said antenna through said coupling means tosaid transmission line, said change being just sufficient to vary thephase of the voltage supplied to the antenna by a proper amount tomaintain the antenna current in a constant phase relation with respectto the voltage supplied to the transmission line.

11. In combination, an antenna, a transmission line, a coupling betweensaid transmission line and antenna, and means operable through saidcoupling means to control the voltage supplied by said transmission lineto maintain the phase of the antenna current constant irrespective ofchanges in antenna capacity.

12. In combination, an antenna, and a transmission line coupled thereto,said transmission line having an electrical length equal to the normalphase displacement between the antenna current and antenna voltage.

13. In combination, a radiating antenna, and a transmission line coupledthereto, and means so arranged that the inductive and capacitivereactance of said antenna is sufiiciently different at the operatingfrequency to cause a load impedance to be presented to said transmissionline of such value that the phase of the voltage at the output end ofsaid transmission line varies in response to variations in antennacapacity by an amount sufficient to prevent variations in phase of theantenna current.

14. In combination, an untuned antenna, a transmission line forsupplying voltage thereto, a coupling betwen said antenna andtransmission line, said transmission line having such a length that theimpedance presented thereto by said coupling means during variations inantenna capacity tends to prevent variations in phase of the antennacurrent.

15. In combination, an antenna, a transmission line, a, coupling betweensaid transmission line and antenna, and means operable through saidcoupling to control the voltage supplied by said transmission line tomaintain a constant phase relationship between the antenna current andthe voltage supplied by said transmission line.

16. In combination, an untuned antenna, a transmission line forsupplying voltage thereto, a coupling between said antenna andtransmission line, said transmission line having such a length that theimpedance presented thereto by said coupling means during variations inantenna capacity tends to prevent variations in the phase of the antennacurrent with respect to the phase of the voltage supplied by saidtransmission HANS RODER.

CERTIFICATE OF CORRECTION.

Patent No. 2,279,062. April 7, 1914.2.

HANS RODER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,second column, lines 67 and 68, for the word "rear" read ---real--; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 16th day of June, A. D. 19!;2.

Henry Van Arsdale', (Seal) Acting Commissioner of Pater-ts.

r CERTIFICATE OF CORRECTION. Patent No. 2,279,062. April 7, 1914.2.

HANS RODER.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,sec-- 0nd column, lines 67' and 68, for the word "rear" read -real'--;and .that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 16th day of June, A. D. 19!;2.

v Henry Van Arsda'le', (Seal) Acting Commissioner of Pater-ts.

